// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CC_LAYERS_VIEWPORT_H_
#define CC_LAYERS_VIEWPORT_H_

#include <memory>

#include "base/gtest_prod_util.h"
#include "base/macros.h"
#include "cc/layers/layer_impl.h"
#include "ui/gfx/geometry/vector2d_f.h"

namespace cc {

class LayerTreeHostImpl;

// Encapsulates gesture handling logic on the viewport layers. The "viewport"
// is made up of two scrolling layers, the inner viewport (visual) and the
// outer viewport (layout) scroll layers. These layers have different scroll
// bubbling behavior from the rest of the layer tree which is encoded in this
// class.
class CC_EXPORT Viewport {
public:
    // If the pinch zoom anchor on the first PinchUpdate is within this length
    // of the screen edge, "snap" the zoom to that edge. Experimentally
    // determined.
    static const int kPinchZoomSnapMarginDips = 100;

    // TODO(tdresser): eventually |consumed_delta| should equal
    // |content_scrolled_delta|. See crbug.com/510045 for details.
    struct ScrollResult {
        gfx::Vector2dF consumed_delta;
        gfx::Vector2dF content_scrolled_delta;
    };

    static std::unique_ptr<Viewport> Create(LayerTreeHostImpl* host_impl);

    // Differs from scrolling in that only the visual viewport is moved, without
    // affecting the browser controls or outer viewport.
    void Pan(const gfx::Vector2dF& delta);

    // Scrolls the viewport, applying the unique bubbling between the inner and
    // outer viewport unless the scroll_outer_viewport bit is off. Scrolls can be
    // consumed by browser controls.
    ScrollResult ScrollBy(const gfx::Vector2dF& delta,
        const gfx::Point& viewport_point,
        bool is_wheel_scroll,
        bool affect_browser_controls,
        bool scroll_outer_viewport);

    // Scrolls the viewport. Unlike the above method, scrolls the inner before
    // the outer viewport. Doesn't affect browser controls or return a result
    // since callers don't need it.
    void ScrollByInnerFirst(const gfx::Vector2dF& delta);

    // Scrolls the viewport, bubbling the delta between the inner and outer
    // viewport. Only animates either of the two viewports.
    gfx::Vector2dF ScrollAnimated(const gfx::Vector2dF& delta,
        base::TimeDelta delayed_by);

    void PinchUpdate(float magnify_delta, const gfx::Point& anchor);
    void PinchEnd();

    // Returns the "representative" viewport layer. That is, the one that's set
    // as the currently scrolling layer when the viewport scrolls and the one used
    // in the scrolling code to indicate scrolling should happen via this class.
    LayerImpl* MainScrollLayer() const;

private:
    explicit Viewport(LayerTreeHostImpl* host_impl);

    // Returns true if viewport_delta is stricly less than pending_delta.
    static bool ShouldAnimateViewport(const gfx::Vector2dF& viewport_delta,
        const gfx::Vector2dF& pending_delta);
    bool ShouldBrowserControlsConsumeScroll(
        const gfx::Vector2dF& scroll_delta) const;
    gfx::Vector2dF AdjustOverscroll(const gfx::Vector2dF& delta) const;

    // Sends the delta to the browser controls, returns the amount applied.
    gfx::Vector2dF ScrollBrowserControls(const gfx::Vector2dF& delta);

    gfx::ScrollOffset MaxTotalScrollOffset() const;
    gfx::ScrollOffset TotalScrollOffset() const;

    LayerImpl* InnerScrollLayer() const;
    LayerImpl* OuterScrollLayer() const;

    void SnapPinchAnchorIfWithinMargin(const gfx::Point& anchor);

    LayerTreeHostImpl* host_impl_;

    bool pinch_zoom_active_;

    // The pinch zoom anchor point is adjusted by this amount during a pinch. This
    // is used to "snap" a pinch-zoom to the edge of the screen.
    gfx::Vector2d pinch_anchor_adjustment_;

    FRIEND_TEST_ALL_PREFIXES(ViewportTest, ShouldAnimateViewport);

    DISALLOW_COPY_AND_ASSIGN(Viewport);
};

} // namespace cc

#endif // CC_LAYERS_VIEWPORT_H_
